Conventionally, after a pattern is formed on a resist deposited on a silicon wafer via exposure, development, rinsing, and drying, a large-scale, high-density, and high-performance device is fabricated through processes of coating, etching, rinsing, and drying. In particular, a resist of a high molecular material is exposed by light, X rays, and an electron beam. In each process, because a fluid, such as a developer or a rinsing liquid, is used especially in a development or rinsing process, a drying process is necessary after a rinsing process.
In this drying process, when the width of space between patterns formed on a resist substrate amounts to less than about 90 nm, Laplace force operates between the patterns by the surface tension (capillarity) of a fluid that is left between the patterns, and pattern collapse occurs. To prevent the pattern collapse caused by the operation of the surface tension of the fluid that is left between the patterns, the drying process for reducing the surface tension that operates between the patterns is used. A method is known, which uses a supercritical fluid of carbon dioxide together with the predetermined pressure vessel shown in JP-A No. 33302/2002.
This conventional drying method that uses supercritical carbon dioxide includes the following basic processes:
(1) A residual liquid in a sample that is insoluble in a fluid in a supercritical state is substituted previously for a rinsing liquid that is soluble in the fluid.
(2) After a sample is installed in a high pressure vessel that works as a drying chamber, the vessel is sealed hermetically. A fluid in a liquid state or supercritical state is introduced into the drying chamber, and a rinsing liquid is substituted for the fluid in the liquid state or supercritical state.
(3) When a fluid in a liquid state is introduced into a drying chamber, the pressure and temperature of the drying chamber are increased to a critical point or more.
(4) A fluid in a supercritical state is drained.
In a conventional drying process, however, when the dimensions, that is, the width of space between patterns formed on a resist substrate amounts to less than about 90 nm, Laplace force operates between the patterns by the surface tension (capillarity) of a fluid that is left between the patterns, and pattern collapse occurred. Still more, if pattern width scales down and amounts to less than about 70 nm even in the drying process that uses a supercritical fluid and a low surface tension rinsing liquid, the pattern collapse cannot be prevented.
Further, a conventional critical point drying method is long in treatment time and requires the time from about several ten minutes to one hour or more. Because a large-diameter substrate having a diameter of 100 mm or more, especially a pattern of less than about 40 nm, is exceedingly inferior in the substitution efficiency of a rinsing liquid and liquid carbon dioxide. Accordingly, because the rinsing liquid that is left between patterns cannot be substituted even if the substitution time of about three hours is set, the surface tension operates between the patterns and pattern collapse can hardly be prevented. Further, the large-caliber substrate could not be dried uniformly.